Among image forming devices such as copy machines, printers, facsimiles, and the like, for forming images using electrophotographic methods, are devices that use contact electrification methods to charge a photoreceptor drum surface by bringing into contact a charging member, such as a roller, a blade, or the like, to which a voltage is applied, with a photoreceptor drum (an image holding body).
Among these contact electrification methods, for preventing non-uniform charging (for charge equalization) of the photoreceptor drum surface, a method (referred to as an AC contact electrification method, below) is known, in which direct voltage (DC electric field) and alternating voltage (AC electric field) are superimposed and applied to the charging member.
In this AC contact electrification method, due to adding the alternating voltage (AC electric field) to the charging member, on account of the electrostatic adsorbability thereof, there are cases in which the charging member and the photoreceptor drum resonate, and extremely jarring noise (resonance noise due to alternating voltage signals) known as charging noise, occurs.
As a preventative measure against this type of charging noise, for example, insertion of an anti-vibration member, such as a weight, rubber, or the like, inside the photoreceptor drum is possible.
Additionally, methods for reducing the charging noise, by the structure, material, or dimensions of the charging member, are proposed.
Methods of preventing the charging noise (resonance) by applying irregular variations (fluctuations) to the frequency of the alternating voltage applied to the charging member, by a chaos generator, are also proposed.
Furthermore, it is proposed to set the frequency of the alternating voltage applied to the charging member as low as possible, in a range in which the occurrence of moiré image interference fringes in image formation can be prevented when forming the images.
However, in the prior art in which an anti-vibration member is inserted in the photoreceptor drum, and in methods in which the charging noise is reduced by the structure of the charging member, there have been problems in that manpower required in manufacturing the photoreceptor drum increases (resulting in higher manufacturing costs), and the charging noise is generated due to changes in the charging member and the photoreceptor drum over time (degradation with time). That is, as a result of variations in elastic resonance frequency of the photoreceptor drum or the charging member, due to changes over time, such as film thickness abrasion in the photoreceptor drum, surface layer abrasion in the charging member, rattling, and the like, there have been potential problems in that resonance occurs at harmonic frequencies of four times or six times the frequency of the alternating voltage applied to the charging member, and extremely jarring charging noise occurs. In these cases, outside of changing the degraded member, there is no strategy for eliminating the charging noise.
In addition, with the method of preventing the charging noise using the chaos generator, since fluctuations are given to the frequency of the applied alternating voltage, there has been a problem in that uniform charging of the photoreceptor drum is impaired.
Moreover, since the method using the chaos generator and the method of setting the frequency of the alternating voltage applied to the charging member low, as described above, in each case, are not in response to the state of the charging noise generation, there has been a problem in that conditions occur in which the charging noise cannot be effectively curtailed, or that the frequency of the applied alternating voltage is varied unnecessarily, so that it adversely affects image quality.
Accordingly, the present invention was made in view of the abovementioned circumstances, and has as an object the provision of an image forming device that uses an AC contact electrification method that can assuredly reduce the generation of the charging noise (resonance noise) according to condition variations, while preventing adverse affects on the image quality.